Mobile communication systems have been developed to provide voice call services, supporting users' mobility. With the development of communication technology, they have recently provided data communication services, or high speed data services. As mobile communication systems evolve to provide more various services, they face lack of resources and users' demands for high speed data services. Therefore, development of more advance mobile communication systems is required.
In order to conform to the requests, standardization of the 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) as the next generation mobile communication system is ongoing. LTE is a technology to implement high speed packet-based communication, up to maximum 100 Mbps. To this end, various proposals have been discussed. As an example, a scheme has been proposed to reduce the number of nodes on communication paths by simplifying network architecture. Another scheme has been proposed to apply wireless protocols to wireless channels.
FIG. 1 is a view of a general LTE mobile communication system.
Referring to FIG. 1, the wireless access network of the LTE mobile communication system includes an evolved Node B or an evolved UTRAN Node B (EUTRAN), hereafter called eNB 110, a Mobility Management Entity (MME) 120, a Serving Gateway (S-GW) 130, etc. User Equipment (UE) 100 is connected to an external network through then eNB 110, the S-GW 130, and a Packet Data Network Gateway or Packet Data Network (PDN) Gateway, hereafter called P-GW 160.
eNB 110 is a Radio Access Network (RAN) node and corresponds to a Radio Network Controller (RNC) of a Universal Terrestrial Radio Access Network (UTRAN) system and a Base Station Controller (BSC) of a GSM EDGE Radio Access Network (GERAN) system. eNB 110 is connected to UE 100 through a wireless channel and performs functions similar to those of a conventional RNC/BSC. eNB 110 may simultaneously cover a number of cells.
In LTE, since the user's traffic and real-time services, such as Voice over IP (VoIP) service, are routed through shared channels, systems are required for collecting status information about UE devices 100 and for scheduling the UE devices. These systems are covered by the eNB 110.
MME 120 performs control functions. One MME 120 may be connected to a number of eNBs.
S-GW 130 provides data bearers. S-GW 130 creates or removes a bearer under the control of the MME 120.
Application Function (AF) 140 exchanges application-related information with a user in a level of application.
Policy Charging and Rules Function (PCRF) 150 controls policy related to a user's Quality of Service (QoS). Policy and Charging Control (PCC) rule corresponding to policy is transmitted to the P-GW 160. Policy Charging and Rules Function (PCRF) 150 is an entity of controlling a QoS for traffic and a charging service. In general, user plane (UP) refers to a path connecting UE 100 and an RAN node, i.e., eNB 110, S-GW 130, and P-GW 160, through which user's data is transmitted/received. The path between UE 100 and eNB 110 uses a wireless channel and is subjected to the limitation of resources.
In a wireless communication system such as LTE, the unit of channel to which QoS can be applied is an Evolved Packet System (EPS) bearer. One EPS bearer is used to transmit IP flows with the same QoS request. An EPS bear may be designated with a parameter related to QoS, including QoS Class Identifier (QCI) and Allocation and Retention Priority (ARP). The QCI is a parameter defining the QoS priority as an integer. The ARP is a parameter to determine whether to accept or refuse the creation of a new EPS bearer.
An EPS bearer corresponds to a Packet Data Protocol (PDP) context of a General Packet Radio Service (GPRS) system. One EPS bearer belongs to PDN. The PDN has an Access Point Name (APN) as an attribute. If PDN connection for an IMS service such as Voice over LTE (VoLTE) is formed, it must be created by using a well-known IMS APN.
In order to support voice calls, LTE networks employ an IMS-based VoLTE technology using a Packet Switched (PS) delivery or a circuit switched fall back (CSFB) technology using a circuit switched (CS) delivery for a 2G/3G system. In LTE networks, the term ‘VoLTE’ has the same concept as ‘Voice over IMS (VoIMS).’